How does groundwater move between underground aquifers and nearby lakes or streams?

Groundwater movement between underground aquifers and surface water bodies like lakes or streams is driven by differences in pressure, which are determined by the relative elevation of the water table compared to the surface water level.12

When a lake or stream intersects the water table, the two systems communicate directly. The direction of flow is governed by the following principles:1

• Groundwater to Surface Water: If the water table is higher than the level of the lake or stream, a pressure head develops that induces groundwater to flow into the surface water body. This groundwater flow often provides the base flow that sustains streams between precipitation events.1
• Surface Water to Groundwater: Conversely, if the water table is lower than the level of the lake or stream, the pressure gradient induces water to flow from the surface body into the groundwater system.1

This continuous exchange is a vital component of the hydrologic cycle, linking subsurface and surface inland water ecosystems.12